Field of the Invention
The invention relates to a method for determining the reception field strength of the RF carriers of adjacent channels and of the current channel in mobile radio apparatus operated in a TDMA system (time-division multiple access system). A plurality of individual measurements are carried out for each RF carrier during a measurement time period, and a representative, determined value is formed from the corresponding individual measured values.
The invention also relates to a mobile radio set for operation in a TDMA system, having RF receiver and transmitter units controlled by a synthesizer, having modulator and demodulator units assigned to an AF unit, having a level measurement and storage unit, having a counter and having a time-dependent controller which is assigned to the synthesizer, to the RF sections, to the demodulator unit and to the level measurement and storage unit, having a frequency reference unit for the synthesizer, counter and time-dependent controller and for the modulator and demodulator units, and having a control logic device for controlling the level measurement and storage unit and other units, the control logic device and the counter being set up with the time-dependent controller and interacting with the RF receiving section, the demodulator and the level measurement and control unit for the purpose of measuring the levels of predetermined RF carriers repeatedly during a measurement time period and of forming a representative value from the determined individual measured values.
Modern mobile radio sets, such as those which operate using the GSM system, regularly have to measure the field strength at predetermined frequencies in order to allow problem-free handover to a new base station. For example, the GSM system uses 124 RF channels, of which the base station to the mobile radio set uses up to 32 RF channels, whose field strength must be checked. The field strengths of the six strongest carriers are always kept up to date in a memory.
The mobile radio set has to carry out a predetermined minimum number of field strength measurements, which should be carried out at times that are distributed as uniformly as possible. The determined measured values, in the GSM system generally five, are used to form a mean value, the intention of which is to avoid misinterpretations, for example as a result of short-term fading or temporary disconnections.
The field strength measurements are carried out during conversation as well as in the so-called idle mode. For this purpose, the base station always transmits at a predetermined frequency, the "C0" frequency in the GSM system, even if this is unnecessary for the actual signalling. Between two corresponding bursts of the TDMA system, the base station may also briefly transmit at a lower power, so that there are field strength reductions between successive bursts (also called "up/down ramping"). With regard to the required field strength measurement, reference is had, for example, to DRAFT pr ETS 300578, May 1995, ETSI (European Telecommunications Standard Institute). Measurement over the duration of a time slot is also based on the GSM Technical Specification, GSM 05.02, August 1996, Version 5.1.0 published by the ETSI. The field strength measurement for adjacent cells and the problems associated with this are also described in Section 4.1.4.3 of the book entitled "The GSM System", M. Mouly and Marie-B. Pautet, Palaiseau 1992.
According to the prior art, the field strength of each C0 channel is measured five times, in each case for the duration of a time slot. The measurement is thereby in general not carried out from the start to the end of a burst. Instead, as the measurement time lasts for the duration of one burst it covers part of one burst and part of the next burst. This is due to the fact that, although the time frames of the individual radio cells have the same burst duration, they are offset with respect to one another.
In the case of network-independent receivers and mobile radio sets, such as those which operate under the GSM Standard, particular value is placed on low power consumption in order to ensure operation for as long as possible with a battery or one accumulator charge, in particular standby operation. Attention is therefore being paid to not carrying out unrequired functions for as long as possible, in order to reduce the mean power consumption. In the case of devices which operate in a radio network using a time-division multiplex organization, a standby mode exists, also called standby operation or the idle mode. In this mode, all the unrequired function groups, for example, can be disconnected periodically from the power supply in order to reduce the mean energy requirement.
The power-consuming functions in the idle mode also include the measurement of the channel field strength. This, of course, disadvantageously reduces the operating duration of the mobile radio set that can be achieved with one accumulator charge.